The present invention relates to a drilling machine, and more particularly, to a drilling machine that applies impacts on a target with a compressed air as a power source.
Conventionally, when drilling a concrete or the like, applying vibrational impacts, in addition to rotational motion, to a drill bit to crush a point of the concrete is known as the fastest drilling method. So as to apply such impacts to a drill bit, generally, part of rotational motion of a motor or the like that rotates a drill bit of a drilling machine is converted to reciprocating motion of a piston etc. arranged in the drilling machine. Then, impacts to be applied to the drill bit are generated from such reciprocating motion of the piston.
However, a drilling machine employing impacts cannot be used at places subject to noise regulation due to noise brought about when applying impacts. As a conventional drilling machine that is intended to be used at places subject to noise regulation with low noise, there is known a drilling machine for concrete structures disclosed in Laid-Open Japanese Utility Model Application Publication No. S62-201642. The drilling machine merely rotates a drill bit made mainly of diamond powder sintered metal, and the main body of the drilling machine is not provided with an impact mechanism for applying impacts to the drill bit.
However, when using a conventional drilling machine employing impacts, since part of motive energy to rotate a drill bit is used as motive energy to generate impacts, motive energy to rotate a drill bit is lowered, and intensity of thus generated impacts cannot be adjusted.
There is raised a problem that, when drilling concrete, the drilling speed of a drilling machine that employs only rotational motion and is not provided with an impact mechanism to apply impacts to a drill bit is extremely lowered when running into a high hardness aggregate such as a coarse aggregate. Furthermore, since the drilling operation is performed using friction generated between the leading end of a drill bit and a-concrete etc., the leading end of the drill bit has to be thrust against the concrete. Accordingly, when drilling a hard aggregate, an especially large thrust is required. In case the drilling operation is performed in a downward direction or in a transverse direction, a thrusting force can be obtained by employing the own weight of a drilling machine or the weight of a drilling worker. On the other hand, in case the drilling operation is performed in an upward direction, a drilling machine has to be uplifted and a load as a thrust has to be applied to the drill bit, which requires a hard labor.
As for drilling operation at places subject to noise regulation, the regulation may be varied depending on work time. Accordingly, for example, at least two drilling machines are required, one of which is for drilling operation employing impacts at a period of time with loosened noise regulation, while the other of which is for drilling operation employing only rotational motion at a period of time with tightened noise regulation. Furthermore, as for noise countermeasures, since a drilling machine has to be selected from only two drilling machines, that is, a drilling machine employing impacts with high noise and a drilling machine employing only rotational motion with low noise, there may be raised a case in which the drilling machine employing impacts cannot clear noise regulation while noise of the drilling machine employing only rotational motion is extremely low as compared with noise set down by noise regulation. In this case, the drilling machine employing only rotational motion alone can be used, which undesirably lowers working efficiency.